Method for the treatment of patent ductus arteriosus

ABSTRACT

A device and method for treating patent ductus arteriosus in a human. A catheter having a collapsible/expandable heating element at a distal end for entering an infant transcutaneously and being advanced to the ductus arteriosus. A method of heating the inner surface of the ductus arteriosus with the heating element to a temperature sufficient to produce a material change in the collagen of the ductus arteriosus such that the ductus arteriosus passage shrinks to closure.

This application is a continuation of application Ser. No. 08/739,820,filed Oct. 30, 1996, now U.S. Pat. No. 5,827,268.

FIELD OF THE INVENTION

The present invention is related generally to the modification of hearttissue for the ligation or interruption of congenital heart defects.

BACKGROUND OF THE INVENTION

Patent ductus arteriosus is a condition resulting from the partialcontinuation of fetal circulation. A fetus does not use its own lungs tooxygenate its blood, rather the fetus' blood bypasses the lungs and isoxygenated by the placenta. The ductus arteriosus allows blood to flowbetween the pulmonary artery and aorta in utero bypassing thenon-functioning lungs during fetal development. Normally, the ductusarteriosus conduit closes naturally. This is prostaglandin dependent. Ifthe ductus remains open, the infant has pathological shunting of bloodfrom the systemic to the pulmonary system. This results in pulmonaryhypertension which if uncorrected can result in the infant's disabilityand death.

Surgical procedures have been developed for closing the ductus whichinvolve open heart surgery. The chest of the infant is opened to exposethe ductus. A suture is tied around the ductus to seal it closed. Forobvious reasons, open heart surgery is not desirable if alternativesexist.

Although other methods of occluding defects, most notably the use of aplastic plug to occlude the defect, were suggested as early as the1950's, such methods similarly require the use of open heart surgery toaccess the defect and place the prosthetic implant.

Beginning in the early 1970's, a number of devices and methods wereproposed for the percutaneous transluminal catheterization procedure forthe repair of intracardiac defects. For example, U.S. Pat. No. 3,874,388to King, et al., describes a device in which a pair of umbrella-likeoccluders are positioned on opposite sides of a defect and drawn andlocked together at a central hub which crosses the defect. Although theKing device and method proposed to eliminate the need to perform openheart surgery, use of the device was complicated in that generally thedevice required the umbrella-like occluders to be opened manually oncepositioned at the defect.

Collagen-containing connective tissue is ubiquitous in the human bodyand demonstrates several unique characteristics not found in othertissues. It provides the cohesiveness of the musculoskeletal system, thestructural integrity of the viscera as well as the elasticity ofintegument. Intermolecular cross links provide collagen connectivetissue with unique physical properties of high tensile strength andsubstantial elasticity. A previously recognized property of collagen isshrinkage of collagen fibers when elevated in temperature. This uniquemolecular response to temperature elevation is the result of rupture ofthe collagen stabilizing cross links and immediate contraction of thecollagen fibers to about one-third of their original linear dimension.Additionally, the caliber of the individual fibers increases greatly,over four fold, without changing the structural integrity of theconnective tissue.

There has been discussion in the existing literature regardingalteration of collagen connective tissue in different parts of the body.One known technique for effective use of this knowledge of theproperties of collagen is through the use of infrared laser energy toeffect tissue heating. The use of infrared laser energy as a cornealcollagen shrinking tool of the eye has been described and relates tolaser keratoplasty, as set forth in U.S. Pat. No. 4,976,709. Theimportance of controlling the localization, timing and intensity oflaser energy delivery is recognized as paramount in providing thedesired soft tissue shrinkage effects without creating excessive damageto the surrounding non-target tissues.

Another known technique of altering collagen is described in U.S. Pat.No. 5,458,596 to treat joints. U.S. Pat. No. 5,437,664 describes using acatheter for venous occlusion and coagulation of blood, but does notcontemplate treating patent ductus arteriosus by shrinking the vessel toclosure.

SUMMARY OF THE INVENTION

The present invention provides a safe, cost-effective method fortreating patent ductus arteriosus in a human using selectively appliedheat. Generally speaking, the present invention provides a device andmethod for treating patent ductus arteriosus in a human. The catheterhas a heating element at a distal end for entering a humantranscutaneously which is advanced to the ductus arteriosus. The methodinvolves heating the inner surface of the ductus arteriosus with theheating element to a temperature sufficient to produce a material changein the collagen of the ductus arteriosus such that the ductus arteriosusconduit shrinks to closure. The treatment is accomplished by applyingheat to the inner surface of the ductus arteriosus to collapse theductus arteriosus passage.

In one aspect of the invention, there is provided a method for closing apatent ductus arteriosus of a patient by entering the vascular system ofthe patient, advancing a catheter having a heating element associatedwith a distal end portion through the vascular system of the patientinto the ductus arteriosus, positioning the heating element within theductus arteriosus at a first position, and energizing the heatingelement to effect a temperature in the ductus arteriosus sufficient toreduce at least a first portion of the ductus arteriosus passage.

In another aspect of the invention, there is provided a method forclosing a patent ductus arteriosus of a patient by entering the vascularsystem of the patient, advancing a catheter comprising a heating elementand moveable sleeve through the vascular system of the patient into theductus arteriosus, positioning a distal end of the catheter within theductus arteriosus at a first position, retracting the sleeve to exposethe heating element to a first portion of an inside surface of theductus arteriosus, energizing the heating element to effect atemperature in the ductus arteriosus sufficient to alter the size of theductus arteriosus passage such that at least the first portion of apassage through the ductus arteriosus is reduced, withdrawing theheating element to further reduce the ductus arteriosus passage with atip of the heating element, retracting the heating element into thesleeve, and withdrawing the catheter from the patient.

In still another aspect of the invention, there is provided an apparatusfor closing a patent ductus arteriosus of a patient having a heatingelement which has a collapsible distal end portion, the distal endportion being collapsible as the ductus arteriosus passage is reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

As used herein, like reference numerals will designate similar elementsin the various embodiments of the present invention wherein:

FIG. 1 is a diagrammatic partial cross-sectional view of a heart with aJ-tipped guidewire inserted through the femoral artery;

FIG. 2 is a diagrammatic partial cross-sectional view of the heart withthe distal end of the J-tipped guidewire advanced to the opening to theductus arteriosus;

FIG. 3 is a diagrammatic partial cross-sectional view of the heart withthe distal end of the J-tipped guidewire located in the ductusarteriosus and a catheter in accordance with one embodiment of thepresent invention being advanced over the J-tipped guidewire;

FIG. 4 is a diagrammatic partial cross-sectional view of the heart withthe distal end of the catheter of FIG. 3 located in the ductusarteriosus;

FIG. 5 is a diagrammatic partial cross-sectional view of the heart witha sleeve of the catheter of FIG. 3 being retracted to expose a portionof a heating element in accordance with one embodiment of the presentinvention;

FIG. 6 is a diagrammatic partial cross-sectional view of a portion ofthe heart with the outer sleeve of FIG. 3 retracted to expose theheating element;

FIG. 7 is a diagrammatic partial cross-sectional view of a portion ofthe heart showing the ductus arteriosus passage collapsing on theheating element;

FIG. 8 is a diagrammatic partial cross-sectional view of the portion ofthe heart showing the ductus arteriosus passage collapsed and theheating element being retracted into the sleeve;

FIG. 9 is a diagrammatic partial cross-sectional view of the heart withthe distal end of a guide catheter of an alternate embodiment located inthe ductus arteriosus;

FIG. 10 is a diagrammatic partial cross-sectional view of a portion ofthe heart with the guide catheter sleeve of FIG. 9 retracted to exposethe expandable heating element;

FIG. 11 is a diagrammatic representation of one embodiment of thecatheter of the present invention with a heating element located in asleeve;

FIG. 12 is a diagrammatic representation of the catheter of FIG. 11 withthe sleeve retracted to expose the heating element;

FIG. 13 is a cross-sectional view taken along line 13--13 of FIG. 11;

FIG. 14 is a diagrammatic representation of another embodiment of thecatheter of the present invention with the heating element located inthe sleeve;

FIG. 15 is a diagrammatic representation of yet another embodiment ofthe catheter of the present invention with the sleeve partiallyretracted to expose a portion of the heating element;

FIG. 16 is a end view taken along line 16--16 of the heating element ofFIG. 15;

FIG. 17 is an end view of an alternate embodiment of the heating elementof FIG. 16;

FIG. 18 is a diagrammatic representation of still another embodiment ofthe catheter of the present invention with the sleeve retracted toexpose the heating element;

FIG. 19 is a diagrammatic representation of yet another embodiment ofthe catheter of the present invention;

FIG. 20 is a diagrammatic representation of still another embodiment ofthe catheter of the present invention; and

FIG. 21 is a diagrammatic representation of another embodiment of thecatheter of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a device and method for effecting changein collagen-containing soft tissue in a patent ductus arteriosus of ahuman. The ductus arteriosus is a vessel having arterial characteristicsin that the ductus arteriosus has two layers of muscular and collagenconnective tissue. The invention accurately controls the application ofheat within a specific thermal range, and delivers thermal energy to thecollagen-containing soft tissue of the ductus arteriosus to close offthe ductus arteriosus to blood flow without ablating the tissue.

Referring initially to FIGS. 1-8 which illustrate the placement ofcatheter 20 within the patent ductus arteriosus 32 of a heart 24.Guidewire 28 (and subsequently catheter 20) is inserted in theillustrated embodiment through a femoral artery 26 or vein using theSeldinger technique or a cut-down technique. Alternatively, theguidewire 28 and subsequently catheter 20 can be inserted through abrachial artery or vein (not shown) in the arm to gain access to theductus arteriosus. The guidewire 30 is advanced through the aorta 30using conventional fluoroscopic guidance. Preferably, the guidewire 28is a J-tipped guidewire to facilitate advancing the guidewire into theopening of the ductus arteriosus 32 (FIG. 2). However, otherconfigurations of guidewires or other techniques can be used to gainentry into the ductus arteriosus 32 by the catheter 20, for examplethrough the vena cava 22. The guidewire 28 is advanced into the ductusarteriosus 32 (FIG. 3). The catheter 20 of the present invention isinserted through the femoral artery 26 and advanced over the guidewire28 using conventional techniques into the ductus arteriosus 32 (FIG. 4).After the distal end 34 of catheter 20 is inserted into the desiredlocation in the ductus arteriosus 32, guidewire 28 is retracted throughthe catheter. The desired location may be a fully inserted position inthe ductus arteriosus 32 as shown in FIG. 4, an intermediate position(not shown) in the ductus arteriosus, or in the opening of the ductusarteriosus (not shown).

Catheter 20 is sufficiently long to extend from a fully insertedposition in the ductus arteriosus 32 to an RF generator 36 locatedremotely from the patient. Catheter 20 has a sleeve 38 that extendsalong a part of that length from a fully inserted position in the ductusarteriosus 32 to a convenient point outside of the insertion point inthe patient such that the surgeon performing the procedure can grasp andmanipulate the sleeve 38. The surgeon retracts the sleeve 38 over aconductor 40 that is connected to RF generator 36 to expose a heatingelement 42 associated with the distal end of the catheter 20.Alternatively, the catheter 20 can be inserted intermediately in theductus arteriosus 32 or at the opening of the ductus arteriosus and theconductor 40 can be pushed out of the distal end of the sleeve 38. Theductus arteriosus generally has a length in the range of 2 millimetersto 3 centimeters, accordingly the length of the collapsible portion ofthe heating element 42 in accordance with any of the embodimentsdescribed below is in the range of about 2 millimeters to about 3centimeters.

Preferably, the outer diameter of the catheter 20 is smaller than theinside diameter of the ductus arteriosus 32 so that the catheter 20passes atraumatically into the ductus arteriosus 32. The heating element42 is expandable (preferably self-expanding) and has an outer diameterlarger than the outer diameter of the catheter 20 and the inner diameterof the ductus arteriosus 32 such that when the surgeon retracts thesleeve 38 (or advances the conductor 40), the heating element 42 expandsto contact the inside surface of the ductus arteriosus 32 (FIG. 6). Theheating element 42 can extend the entire length of the ductus arteriosus32 as shown in FIGS. 6-8, or can extend only along a portion of theductus arteriosus. In the second situation, the steps described belowcould be repeated as many times as desired by the surgeon to accomplishclosure along the length of the ductus arteriosus. The heating element42 is energized to bring about shrinkage of the ductus arteriosuspassage such that the ductus arteriosus closes around the heatingelement which in turn also collapses.

Referring to FIGS. 9 and 10, an alternate embodiment for the catheter 20and method of placement of the catheter 20 within the patent ductusarteriosus 32 of a heart 24 is shown. A guidewire (not shown) isinserted and advanced to the ductus arteriosus using conventionalfluoroscopic guidance as described above through a femoral artery 26 orvein using the Seldinger technique or a cut-down technique.Alternatively, the guidewire and subsequently catheter 20 can beinserted through a brachial artery or vein (not shown) in the arm togain access to the ductus arteriosus. A guide sleeve 62 is insertedthrough the femoral artery 26 and advanced over the guidewire (notshown) using conventional techniques into the ductus arteriosus. Afterthe distal end 64 of guide sleeve 62 is inserted into the desiredlocation in the ductus arteriosus 32, the guidewire is retracted throughthe guide sleeve. The desired location may be a fully inserted positionin the ductus arteriosus 32 as shown in FIG. 9, an intermediate position(not shown) in the ductus arteriosus, or in the opening of the ductusarteriosus (not shown). Catheter 20 is then inserted into and advancedthrough the guide sleeve 62 to the desired location using conventionalfluoroscopic techniques.

Catheter 20 is sufficiently long to extend from a fully insertedposition in the ductus arteriosus 32 to an RF generator 36 locatedremotely from the patient (FIG. 10). Guide sleeve 62 has a length thatextends along a part of the catheter length from a fully insertedposition in the ductus arteriosus 32 to a convenient point outside ofthe insertion point in the patient such that the surgeon performing theprocedure can grasp and manipulate the guide sleeve 62. The surgeonretracts the guide sleeve 62 over the catheter 20 that is connected toRF generator 36 to expose the heating element 42 associated with thedistal end of the catheter 20. Alternatively, the guide sleeve 62 can beinserted intermediately in the ductus arteriosus 32 or at the opening ofthe ductus arteriosus and the catheter 20 can be pushed out of thedistal end of the guide sleeve 62.

Preferably, the outer diameter of the guide sleeve 62 is smaller thanthe inside diameter of the ductus arteriosus 32 so that the guide sleeve62 passes atraumatically into the ductus arteriosus 32 over theguidewire (not shown). Preferably, the heating element 42 is expandable(preferably self-expanding) and has an outer diameter larger than theouter diameter (accordingly, the inner diameter) of the guide sleeve 62such that the heating element is compressed as it is inserted throughthe guide sleeve. Likewise, the heating element 42 has an outer diameterlarger than the inner diameter of the ductus arteriosus 32 such thatwhen the surgeon retracts the guide sleeve 62 (or advances the catheter20), the heating element 42 expands to contact the inside surface of theductus arteriosus 32 (FIG. 10). The heating element 42 can extend theentire length of the ductus arteriosus 32 as shown in FIGS. 6-8, or canextend only along a portion of the ductus arteriosus as shown in FIGS.9-10.

After completing the procedure for closing off the ductus arteriosus,the heating element 42 is withdrawn into the sleeve 38 and the catheter20 is then removed from the patient. The access point for the guidewireand catheter is sutured closed if a cutdown had been performed, or localpressure is applied until bleeding is controlled if the Seldingertechnique was used. A bandage is then applied. A pressure dressing maybe applied if necessary.

Preferably, heating element 42 is an RF electrode located at the distalend of the catheter 20. Alternatively, the method is contemplated to beused with any suitable appliance for applying radiant energy, thermalenergy, or to otherwise heat the tissue in a patent ductus arteriosusand shrink the ductus arteriosus conduit to closure. When the heatingelement 42 of the catheter 20 is positioned at the treatment site of thepatent ductus arteriosus 32, the RF generator 36 is activated to providesuitable RF energy, preferably at a selected frequency in the range of10 megahertz to 1000 megahertz. One criteria for the selection of theapplied frequency is the absence or minimization of coagulation in theductus arteriosus. The emitted energy is converted within the tissue ofthe ductus arteriosus into heat in the range of about 50 degrees Celsiusto about 98 degrees Celsius. As the temperature of the ductus arteriosustissue increases, the ductus arteriosus passage begins to shrink withoutrupture or perforation of the ductus arteriosus. The shrinkage isapparently due, without being limited to a theory, in part todehydration and in part to the structural transfiguration of thecollagen fibers in the vessel. Although the collagen becomes compactedduring this process, the collagen still retains some elasticity. When RFenergy is applied, shrinkage of the ductus arteriosus reduces thepatency. As the ductus arteriosus 32 shrinks inward on the heatingelement 32, the heating element collapses to a diameter just greaterthan the diameter of the conductor 40. As the heating element 32collapses to a diameter just greater than the diameter of the conductor40, the conductor 40 is withdrawn. As the conductor 40 is withdrawn, theremainder of the ductus arteriosus will close at the distal tip of theheating element 32 as the tip becomes the focal point of the current. Inthis way, the focusing of the heat at the tip of the heating elementcloses off the ductus arteriosus.

RF energy is no longer applied after there has been sufficient shrinkageof the ductus arteriosus passage to close off the ductus arteriosus tothe flow of blood. Sufficient shrinkage may be detected by fluoroscopy,external ultrasound scanning, pulse-echo ultrasound scanning, sensingthe collapsing or straightening of the heating element with appropriatefeed back variables, impedance monitoring, temperature monitoring,direct visualization using an angioscope, or any other suitable method.

Substantial shrinkage may be achieved very rapidly, depending upon thespecific treatment conditions. Because the shrinkage can proceed at arather rapid rate, the RF energy is preferably applied at low powerlevels. The RF power is preferably applied in the range of about 1 wattto about 10 watts. Preferably, the RF energy is applied for a length oftime in the range of about 10 seconds to about 120 seconds. Thefrequency of the RF energy is selected to minimize coagulation at thetreatment site. Suitable RF power sources are commercially available andwell known to those skilled in the art. In one embodiment of theinvention RF generator 36 has a single channel, delivering approximately1 to 10 watts of RF energy and possessing continued flow capability. Therate of shrinkage of the ductus arteriosus can be controlled byincreasing or decreasing blood flow/infusion around the catheter,varying the energy delivered to the heating element, and/or selectingstiffer or more flexible collapsible elements for the heating element tostent the ductus arteriosus while the ductus arteriosus shrinks closed.

The heating element 42 can be made to provide protection againstoverheating of the ductus arteriosus. In one embodiment, the heatingelement has a shape memory capability such that the heating elementself-straightens or collapses if the heating element or the bloodreaches a temperature above 98 degrees Celsius such that contact withthe inner surface of the ductus arteriosus would be lost, the heatingelement would cover with coagulum and the current flow through theheating element would become nearly zero.

The catheter 20 and heating element 42 preferably are constructed frommaterials which would allow visualization under fluoroscopy, x-ray,ultrasound, or other imaging techniques. Preferably, closure of theductus arteriosus is detected by fluoroscopy or external ultrasoundtechniques. For example, a contrast medium may be injected into theductus arteriosus to assess the condition of the ductus arteriosus andthe relationship of the catheter to the treatment area of the ductusarteriosus by contrast radiography during the closure process. Thecatheter 20 can be configured to deliver x-ray contrast medium to allowvisualization by fluoroscopy. As an alternative to fluoroscopy, externalultrasounding techniques such as B-mode scanning using distinctultrasound signals from different angles, can be used to acquire a moremulti-dimensional view of the ductus arteriosus shrinkage at thetreatment site, which improves the detection of uneven shrinkage in theductus arteriosus. An angioscope may also be used to directly visualizeand determine the extent and degree of ductus arteriosus closure. Theshrinkage can be monitored and the collapsing of the heating elementcontrolled to ensure the heating element remains in contact with theductus arteriosus during the process.

Other techniques, for example, temperature monitoring, impedancemonitoring, and ultrasonic pulse echoing, can be utilized in a systemwhich shuts down the application of energy from the heating element tothe ductus arteriosus section when sufficient closure of the ductusarteriosus is detected and to avoid burning of the ductus arteriosus.Monitoring these values for feedback control of the energy applied alsominimizes coagulation. The amount of energy applied can be decreased oreliminated (manually or automatically) if coagulation begins to occur.For example, the temperature of the blood, ductus arteriosus tissue, orof heating element 42 is monitored and the energy being applied adjustedaccordingly. The surgeon can, if desired, override the feedback controlsystem. A microprocessor can be included and incorporated into thefeedback control system to switch the power on and off, as well asmodulate the power. The microprocessor can serve as a controller towatch the temperature and modulate the power in order to minimizecoagulation.

Although the invention has been described as using RF energy forenergizing the heating element, it is to be understood that other formsof energy such as alternating current, microwaves, ultrasound, and light(either coherent or incoherent sources) can be used, and that thethermal energy generated from a resistive coil, a hot fluid element(e.g.,liquids, gases, combinations of liquids and gases, etc.), a curiepoint element, or similar elements can be used as well. The delivery ofthe thermal energy to the ductus arteriosus should be delivered in sucha way that none of the tissue is ablated and/or the collapsing of theductus arteriosus passage occurs without rupture or perforation of theductus arteriosus.

Referring now to FIGS. 11-13, an embodiment of the catheter 20 is shownhaving a heating element 42 disposed within a dual lumen sleeve 38 atthe tapered distal end 34 of the catheter. The sleeve 38 is soft andflexible so as to be passed atraumatically through the vascular systemto the ductus arteriosus and so as to be able to traverse the tortuouspath of the vascular system to the ductus arteriosus. Catheter 20 has anoutside diameter in the range of about 1.5 millimeters to 7 millimeters.

Heating element 42 as illustrated in FIGS. 11 and 12 is an expandableand collapsible heating element of a curled configuration (e.g., ahelix, coil, corkscrew, spiral, twist, etc.). Preferably, the heatingelement is a biocompatible material with at least partial shape memorycapability, such as a nickel-titanium-based alloy. Heating element 42 inaccordance with any of the embodiments can be a number of differentmaterials including but not limited to conductive polymer, stainlesssteel, platinum, other noble metals, or shape memory alloy, such asnickel-titanium-alloy (Nitinol™ commercially available from RaychemCorporation, Menlo Park, Calif.).

The heating element 42 and its corresponding conductor 40 are slidablewithin first lumen 44 of sleeve 38. Second lumen 46 slidably receives aguidewire so that catheter 20 can be advanced to the ductus arteriosusover the guidewire as described previously. The inside diameter of firstlumen 44 is smaller than the outside diameter of the expanded, curledheating element 42 as shown in FIG. 12. As a result, when the curledheating element 42 is retracted into the first lumen 44 of sleeve 38,the curl becomes compressed and elongated as shown in FIG. 11.Correspondingly, as the sleeve 38 is retracted to expose the curledheating element 42 as shown in FIG. 12 the heating element 42 expands tocontact the inside surface of the ductus arteriosus as describedpreviously. The diameter of the first lumen is preferably in the rangeof about 2 French to 7 French. The diameter of the second lumen ispreferably in the range of about 0.015 inches to 0.030 inches. Thediameter of the expanded heating element is preferably in the range ofabout 1.5 millimeters to 7 millimeters.

Referring now to FIGS. 15 and 16, there is another embodiment of thecatheter 20 (as shown in FIGS. 1-8) having a heating element 42 disposedwithin a sleeve 38 at the tapered distal end 34 of the catheter. Asdescribed above, the sleeve 38 is soft and flexible. Catheter 20 of thisembodiment has an outside diameter in the range of about 1.5 millimetersto 7 millimeters.

Heating element 42 as illustrated in FIGS. 15 and 16 is an expandableand collapsible heating element comprised of a plurality of conductiveelements 48 (e.g., soft bristles, fibers, "hairs", etc.). The conductiveelements 48 are soft and pliable so as to not perforate or otherwisedamage the ductus arteriosus and so as to be collapsible. The heatingelement 42 and its corresponding conductor 40 are slidable within lumen50 of sleeve 38. Inside of heating element 42 and its correspondingconductor 40 is lumen 52 which slidably receives a guidewire. The insidediameter of lumen 50 is smaller than the outside diameter of theexpandable heating element 42 as shown in FIG. 15. As a result, when theexpandable heating element 42 is retracted into the lumen 50 of sleeve38, the conductive elements 48 are forced to fold down. Correspondingly,as the sleeve 38 is retracted to expose the expandable heating element42 the conductive elements 48 expand to contact the inside surface ofthe ductus arteriosus. The diameter of the lumen 50 is preferably in therange of about 2 French to 7 French. The diameter of the lumen 52 ispreferably in the range of about 0.015 inches to 0.030 inches. Thediameter of the expanded heating element is preferably in the range ofabout 1.5 millimeters to 7 millimeters.

In FIG. 14, there is illustrated an embodiment similar to FIGS. 15 and16, except that the expandable and collapsible heating element 42 andconductor 40 are smaller in diameter and thus do not have a lumenthrough their length thereof. For this embodiment, a dual lumen sleeve38 as described with respect to FIGS. 11-13 is used so that expandableheating element 42 and conductor 40 slide in first lumen 44 and aguidewire (not shown) can be used in the second lumen 46.

The heating element 42, as shown in FIGS. 1-16, operates as a unipolar,internal electrode in the patient's body. An outer electrode (not shown)having a much larger surface area than the heating element 42 is placedon the outer surface of the patient's body. For example, an externalmetal mesh or solid plate is placed on the skin. Both electrodes areconnected to RF generator 36 which produces an electric field at a highfrequency within the patient's body. Because the surface area of theheating element 42 is much smaller than that of the outer electrode, thedensity of the high frequency electric field is much higher around theheating element. The electric field reaches its highest density betweenthe two electrodes in the region near the heating element 42. Theincreased density of the field around the heating element 42 produceslocalized heating of the tissue of the ductus arteriosus.

A bipolar electrode as shown in FIG. 17 can also be used. The heatingelement 42 and conductor 40 are similar to that described with respectto FIGS. 15 and 16 with a plurality of conductive elements and lumen 52,except that in the embodiment of FIG. 17 the conductive elements aredivided into a first set of conductive elements 54 and a second set ofconductive elements 56. In the bipolar arrangement, the heating element42 emits RF energy with the first set of conductive elements 54 and thesecond set of conductive elements 56. The first set of conductiveelements 54 can act as the active electrode, and the second set ofconductive elements 56 can act as the return electrode, or vice versa.An insulator 58 is located between the first set of conductive elements54 and the second set of conductive elements 56. While the conductiveelements 54 and 56 have been shown as soft bristles, fibers, or "hairs",other configurations and arrangements can be used. For example, as shownin FIG. 18, a plurality of loops 60 can be used as the conductiveelements in either a unipolar or bipolar configuration. Similarly, anyof the conductive elements 48, 54, 56 and/or 60 can be angled rearward(as shown), forward, both, or not angled. The bipolar arrangement ofactive and return elements can be twisted around the conductive element40 to distribute the positively and negatively charged elements aroundthe catheter. Any of the conductive elements 48, 54, 56 and/or 60 can beelectrically conductive materials or can be non-conductive materials(such as mylar, PTFE, etc.) coated with graphite or other electricallyconductive coating.

FIG. 19 is a diagrammatic representation of another embodiment of thepresent invention wherein the expandable and collapsible heating element42 like that described with respect to FIG. 14 is heated with a lightsource 66, for example, a laser or halogen source. The light source 66transmits light via fiber optic light pipe 68 to lens 70 which diffusesthe light onto parabolic heat sink 72 to convert the light energy toheat in the heating element 42.

FIG. 20 is a diagrammatic representation of a resistive heating elementembodiment of the present invention. Heating element 42 is a expandableand collapsible coil which is connected to an energy control box 74which provides resistive heating to the coil. An optional protectivesheath 76 (such as Teflon®) can be provided over the heating element.

FIG. 21 is a diagrammatic representation of a hot fluid heating element42 and control box 78 for controlling and regulating the heat applied.Hot fluid is injected into the balloon heating element 42 and circulatedout through the cooler side of the catheter 20. As the ductus arteriosuspassage closes, the balloon heating element 42 collapses and less fluidis circulated through the heating element 42 as the volume of theheating element 42 decreases. Control box 78 has a temperature gauge 80and pressure gauge 82 for monitoring the temperature and pressure,respectively, of the heating element 42. The control box 78 maintainsthe pressure at a constant level by controlling the circulation rate ofa pump (not shown). As the ductus arteriosus closes, the volume of theballoon heating element 42 decreases increasing the pressure in theballoon. The control box 78 decreases the flow of the hot fluid inresponse to the increase in pressure in the balloon.

While several particular embodiments of the invention have beenillustrated and described, it will be apparent that variousmodifications can be made without departing from the spirit and scope ofthe invention. Accordingly, it is not intended that the invention belimited, except as by the appended claims.

What is claimed is:
 1. A method for closing a patent ductus arteriosusof a patient, comprising the steps of:entering the vascular system ofthe patient; advancing a catheter having a non-laser heating elementassociated with a distal end portion through the vascular system of thepatient into the ductus arteriosus; positioning the heating elementwithin the ductus arteriosus at a first position; and energizing theheating element to reduce at least the first portion of the ductusarteriosus without ablating tissue of the ductus arteriosus.
 2. Themethod of claim 1 further comprising:withdrawing the catheter asufficient distance to position the heating element at a secondposition; and energizing the heating element to a temperature sufficientto reduce at least a second portion of the ductus arteriosus.
 3. Themethod of claim 1 further comprising:sensing a predetermined parameter;and automatically decreasing the magnitude of the energy being deliveredby the heating element when the predetermined parameter reaches apreselected value.
 4. The method of claim 1 wherein the non-laserheating element is energized by applying radio frequency electricenergy.
 5. The method of claim 4 wherein the power of the radiofrequency electric energy applied is in the range of about 1 watt toabout 10 watts.
 6. The method of claim 1 wherein the radio frequencyelectric energy is applied for a length of time in the range of about 10to about 120 seconds.
 7. The method of claim 1 furthercomprising:focusing the energy at a distal most portion of the heatingelement as the ductus arteriosus closes.
 8. The method of claim 1wherein the energizing step comprises controlling the amount of energyapplied such that closing occurs without rupturing or perforating theductus arteriosus.
 9. The method of claim 1 wherein the heating elementis energized to a temperature in the range of about 50 degrees Celsiusto about 98 degrees Celsius.
 10. The method of claim 1 furthercomprising sensing the closing of the ductus arteriosus.
 11. The methodof claim 1 further comprising maintaining the heating element in contactwith the ductus arteriosus as the at least first portion of the ductusarteriosus closes.